1. Field of the Invention
The present invention relates to an air supply system for a fuel cell used in a fuel cell system.
2. Description of the Related Art
A fuel cell system used for an automotive vehicle includes a fuel cell and an air supply system for a fuel cell connected to the fuel cell (Japanese Unexamined Patent Publication No. 7-14599).
Specifically, a fuel supply pipe and an air supply pipe for supplying the fuel and the air, respectively, are connected upstream of the fuel cell. The air supply pipe is opened to the atmosphere through a compressor driven by a motor, so that the air constituting an oxygen-containing gas in the atmosphere is compressed to a predetermined pressure in the compression chamber of the compressor and supplied to the fuel cell. This compressor makes up an air supply mechanism as a part of the air supply system for the fuel cell and the compression chamber of the compressor constitutes an air supply chamber.
An air discharge pipe for discharging into the atmosphere the exhaust gas constituting the air from which oxygen is consumed in the fuel cell is connected downstream of the fuel cell. The air discharge pipe is opened to the atmosphere through a regenerator configured integrally with the compressor and, therefore, the exhaust gas is expanded in the regeneration chamber thereby to drive the regenerator and thus assist the compressor. The exhaust gas in the air discharge pipe is produced by reaction in the fuel cell, and therefore contains water vapor generated in the fuel cell as well as water vapor from the atmosphere. For this reason, the air supply system for the fuel cell includes a liquid separator in addition to the compressor and the regenerator described above. The liquid separator is connected with an air discharge pipe, and separates the water vapor as water from the exhaust gas passing through the air discharge pipe. The water thus produced is stored in a storage vessel and then injected into the compression chamber of the compressor by a pump to seal and cool the compression chamber. The liquid separator, the storage vessel and the pump make up a water supply mechanism as the remaining part of the air supply system for the fuel cell. In this way, the air supply system for the fuel cell improves the compression efficiency of the compressor and hence the power generation efficiency of the fuel cell.
In the conventional air supply system for a fuel cell described above, however, the compressor and the regenerator, though integrated with each other, are separated from the liquid separator, the storage vessel and the pump. Therefore, the structure is not sufficiently simplified, thereby increasing the production cost of the air supply system for the fuel cell. Especially, the need for the liquid separator tends to complicate the system. This air supply system for the fuel cell, if used for an automotive vehicle, is unavoidably disadvantageous from the viewpoint of mountability due to its large size.
The present invention has been developed to solve this problem and the object thereof is to provide a sufficiently simplified air supply system for a fuel cell which is low in production cost and which is capable of maintaining the power generation efficiency of the fuel cell.
According to one aspect of the present invention, there is provided an air supply system for a fuel cell comprising an air supply mechanism including an air supply chamber capable of supplying an oxygen-containing gas to a fuel cell and a water supply mechanism for supplying water to the air supply mechanism to close and cool the air supply chamber, wherein the water supply mechanism supplies water to the air supply mechanism by separating it from the exhaust gas discharged from the fuel cell, and the air supply mechanism is integrated with the water supply mechanism.
In the air supply system for a fuel cell according to this aspect of the invention, the water supply mechanism separates water from the exhaust gas discharged from the fuel cell, and the water is supplied to the air supply mechanism. Specifically, the water supply mechanism functions as a liquid separator, a storage vessel and a pump in the prior art. Since the water supply mechanism is integrated with the air supply mechanism, the structure is sufficiently simplified and therefore the production cost of the air supply system for the fuel cell can be reduced. Especially the air supply system for the fuel cell, if used with an automotive vehicle, can be advantageously mounted on the vehicle due to its simplicity.
In this way, with the air supply system for the fuel cell according to the invention, the power generation efficiency of the fuel cell can be maintained while sufficiently simplifying the structure, and reducing the production cost, of the fuel cell.
According to another aspect of the invention, there is provided an air supply system for a fuel cell wherein at least the drive source such as a motor for driving the air supply mechanism is also integrated with the air supply mechanism and the water supply mechanism. By doing so, the structure is further simplified for a further reduced production cost. This simplified structure also improves the mountability of the air supply system for the fuel cell, if used in an automotive vehicle.
The air supply mechanism includes an air supply chamber capable of supplying an oxygen-containing gas to the fuel cell. The air supply mechanism can be of any of various types including a scroll, a vane, a screw, a root and a piston type. The scroll-type air supply mechanism, the vane-type air supply mechanism and the piston-type air supply mechanism, in which the volume of the closed space is reduced, implement the air supply chamber as a compression chamber. The screw-type air supply mechanism and the root-type air supply mechanism, on the other hand, do not reduce the volume of the closed space but supply the gas under pressure and, therefore, implement the air supply chamber as a pressurized supply chamber.
The air supply mechanism is desirably capable of changing the amount of the oxygen-containing gas per unit power. By doing so, the amount of the oxygen-containing gas supplied to the fuel cell can be changed as required, and wasteful power consumption can be avoided for a further improved mechanical efficiency.
The water supply mechanism can include a liquefying unit for liquefying, into water, the water vapor contained in the exhaust gas discharged from the fuel cell. The liquefying unit can be of a centrifugal separation type in which a turbulent flow of the exhaust gas is generated by centrifugal force and collides with the peripheral surface for liquefying the water vapor into water.
On the other hand, the water supply mechanism can include a regeneration mechanism unit for assisting the air supply mechanism by expanding the exhaust gas. The regeneration mechanism includes a regeneration chamber capable of supplying the water generated by expansion of the exhaust gas to the air supply mechanism. Specifically, the exhaust gas is reduced in temperature by expansion, and the water vapor contained in it is liquefied into water. Thus, the regeneration mechanism can function as a water supply mechanism. By doing so, water is supplied from the regeneration chamber of the regeneration mechanism to the air supply mechanism to close and cool the air supply chamber. Therefore, the regeneration mechanism is easily integrated with the air supply mechanism, and a need for a liquid separator is eliminated. In this way, the system is further simplified and the production cost of the air supply system for a fuel cell can be further reduced. In this case, the power generated by the regeneration mechanism adds to the power for activating the air supply mechanism. Specifically, the regeneration mechanism recovers the residual energy from the exhaust gas of the fuel cell and adds it to the power of the air supply mechanism. As a result, wasteful power consumption is avoided for a further improved mechanical efficiency.
The water supply mechanism, desirably, can change the amount of water supplied. By doing so, the amount of water supplied to the air supply mechanism can be changed as required, and therefore the optimum power generation efficiency can be realized.
The air supply mechanism and the regeneration mechanism can be configured to operate on different drive shafts and can be connected to each other through a power transmission mechanism. As an alternative, the air supply mechanism and the regeneration mechanism can be configured to operate on the same drive shaft. The drive shaft is desirably shared by the motor or the like drive source. By doing so, the simplified structure can further reduce the production cost.
The drive source can be an internal combustion engine instead of a motor. In the case where both the motor and the internal combustion engine are used as drive sources, an electromagnetic clutch is desirably arranged between the internal combustion engine and at least the drive shaft of the air supply mechanism. In the case where this air supply system for the fuel cell is mounted on a hybrid car or the like, the mode for driving at least the air supply mechanism by the motor and the mode for driving at least the air supply mechanism by the internal combustion engine can be switched other easily.
Also, the air supply mechanism and the regeneration mechanism are desirably configured to operate on the same drive shaft. The resulting simplified structure can further reduce the production cost.
At least one of the air supply mechanism and the regeneration mechanism is desirably of a scroll type. In that case, the effects described above can be exhibited while at the same time making it possible to achieve a quiet and lightweight air supply system for the fuel cell.
According to yet another aspect of the invention, there is provided an air supply system for a fuel cell comprising an air supply mechanism and a regeneration mechanism of scroll type, wherein the air supply mechanism preferably includes a housing, one surface of the side plate orbiting about a drive shaft and a first spiral member protruded from the same one surface, and the regeneration mechanism preferably includes a housing, the other surface of the same side plate and a second spiral member protruded from the same other surface. In this air supply system for the fuel cell, the side plate from which the first and second spiral members protrude can be shared by the air supply mechanism and the regeneration mechanism of scroll type. As a result, the structure can be considerably simplified and the production cost can be reduced. Also, the total axial length including the drive source such as the motor can be reduced, thereby attaining a superior mountability on a automotive vehicle, for example.
Further, at least one of the air supply mechanism and the regeneration mechanism is desirably of vane type. In that case, the air supply system for the fuel cell, though somewhat less quiet, can achieve an operation and effects similar to those of scroll type.
According to a further aspect of the invention, there is provided an air supply system for a fuel cell comprising an air supply mechanism and a regeneration mechanism of vane type, wherein the air supply mechanism includes a housing, a first rotor rotated by a drive shaft and a first vane adapted to protrude in a radial direction from the first rotor, and the regeneration mechanism includes a housing, a second rotor rotating on the same axis as the first rotor and a second vane adapted to protrude in a radial direction from the second rotor. In this air supply system for the fuel cell, the first rotor and the second rotor have the same structure, and therefore the production cost is reduced.
The present invention will be more fully understood with reference to the accompanying drawings and the preferred embodiments of the invention.